Let these equal $\displaystyle \tau_2 $, $\displaystyle \tau_3 $ and $\displaystyle \tau_5 $ respectively. Show that these elements have order 2 in the group $\displaystyle G(E/\mathbb{Q}) $. So just square the elements and verify that you get the identity?

What is the subgroup $\displaystyle H $ of $\displaystyle G(E/ \mathbb{Q}) $ generated by the elements?